Cores from deep stratigraphic test wells provide an excellent basis for determination of source-rock quality and thermal maturity of potential hydrocarbon source rocks in the Palo Duro Basin. Total organic carbon (TOC) content in Pennsylvanian and Wolfcampian rocks is highest in basinal shales. TOC values greater than 0.5 percent are common, which indicates that Palo Duro Basin shales contain sufficient organic matter to serve as source beds. Microscopic identification indicates that vitrinite, herbaceous material, and amorphous organic matter are the most abundant types of kerogen.
The San Andres Formation in the Palo Duro Basin is a middle Permian carbonate-evaporite sequence situated between two red-bed units, the underlying Glorieta and the overlying undifferentiated Queen-Grayburg sequences. The San Andres Formation, deposited during relative structural quiescence in the region, is composed of cyclic sequences of dark anhydritic mudstone, skeletal limestone, dolomite, nodular anhydrite, bedded anhydrite, and halite.
The State-owned submerged lands of Texas encompass almost 6,000 mi2 (15,540 km2). They lie below waters of the bay-estuary-lagoon system and the Gulf of Mexico and extend 10.3 mi (16.6 km) seaward from the Gulf shoreline (fig. 1). The importance of these lands and their resources to resident flora and fauna as well as to people is well known and documented; more than one-third of the state's population is concentrated within an area of the Coastal Zone that is only about one-sixteenth of the state's land area.
The Van Horn Mountains caldera is a small (~10-km2) igneous center in the Trans-Pecos volcanic province. The caldera formed 37 to 38 mya during eruption of the first of two ash-flow tuffs related to the caldera. Part of the first tuff ponded within the caldera; the lower marker horizon of the Chambers Tuff in the Sierra Vieja south of the Van Horn Mountains is probably the correlative outflow tuff. Following collapse, the caldera was partly filled by a heterogeneous assemblage of air-fall tuff, tuffaceous sediment, and possible ash-flow tuff.
This folded transparent map is at the same scale as its corresponding Geologic Atlas of Texas (GAT) sheet and can be superimposed on it to compare gravity information with surface geology.